1. Field of the Invention
The present invention relates to a method for mask fabrication used in the process of lithography which is one of the fabrication processes for fabricating a semiconductor, and more particularly to a phase shift mask using phase shift material.
2. Description of the Prior Art
A photolithography process, one of the fabrication processes for a semiconductor, is a technique for delineating a designated pattern upon a photoresist film coated over a wafer surface, using a mask and stepper. A phase shift mask used in the photolithography process could result in a better resolution than one which results from a conventional mask fabricated with chrome film. This enables ultra micro pattern formation as required for high integration of semiconductor devices.
Referring to FIG. 1, phase shift material will be briefly explained. Intensity distribution curve 2 of exposure light resulting from phase shift material 1 shows that the intensity of exposure light is reduced at the lateral edge of phase shift material 1 which has phase changes from 0.degree. to 180.degree., and that the use of positive photoresist film results in photoresist patterns at the lateral edge of phase shift material.
FIG. 2 shows a cross sectional view of a traditional phase shift mask and an intensity distribution curve of exposure light passing through the phase shift mask. A phase shift mask, on quartz 4 is formed with chrome patterns 3. A phase shift mask pattern covers not only the space between one chrome pattern and the most adjacent chrome pattern but also a designated part of said two chrome patterns.
The lateral edge of phase shift material 1 with phase changes from 0.degree. to 180.degree. on the chrome film has the advantage of compensating the reduction of resolution occurring when only chrome 3 film is used.
As shown in FIG. 2, the intensity of light 2' passing through the peripheral sites of the mask is less than the intensity of light 2" passing through the central part of the mask, hence resulting in the different critical dimension of the patterns between the central patterns and the peripheral patterns of the photoresist film.